Blood Patterns
Forensic Science
A Brief Intro to Blood Spatter
Analysis
• Blood contains DNA, so it is possible to
identify its exact source.
• The shape of the spatter indicates:
1. the point of origin
2. direction of travel, and
3. angle of impact.
• Certain chemicals can detect the
presence of blood even when it is not
visible
BLOOD TYPES
• Four types of blood- A, B, AB, O
Type
Type
Type
Type
A contains the A proteins
B contains the B proteins
AB contains both A & B proteins
O contains neither A nor B proteins
The Rh Factor
• This is the + or – after the blood type
A+, A-, O+, O-…and so on.
+ means the Rh protein is present,
- means the Rh protein is absent
BLOOD COMPATIBILITY
• Type O- is the universal donor- all other
blood types can accept type O blood
• Type AB+ is the universal recipient- it
can take all other types of blood
MORE ON COMPATIBILITY
Type
Type
Type
Type
Type
Type
Type
Type
O+: takes O- or O+
O-: takes OA+: takes A+, A-, O+ or OA-: takes A- or OB+: takes B+, B-, O+ or OB-: takes B- or OAB+: takes A+, A-, B+, B-, AB+, AB-, O+, OAB-: takes A-, B-, AB-, O-
Basic Info on Shapes of Drops
• The “tail” points in the direction of travel.
• Drop at 90 degree angle will be circular.
• Drop at less than 90 degree angle will be
elliptical
PRESERVING BLOOD EVIDENCE
• Never place bloody evidence in
plastic…it could promote mold
growth and destroy the sample.
• Blood soaked evidence should
be placed in paper.
NEXT: EXAMPLES OF BLOOD SPATTERS
Arterial Blood
Cast Off
Drip
Flow Pattern
Hair Pattern
Low Velocity
Medium Velocity
High Velocity
Swipe Pattern
Transfer from Hammer
Transfer from Screwdriver
Transfer from Fingers
Transfer from Footwear
Transfer from Knife Blade
Wipe from Drying Blood Drop
The End
References:
Forensic Science: An Introduction to
Scientific and Investigative Techniques by
Stuart H. James & Jon J. Nordby
Images from www.peelpolice.on.ca